How cars sound has always been very important. The deep, troaty sound of the five cylinder petrol engine of my faithful Volvo 850 proves amply the point. Whenever you drive it out of an underground garage, or in a narrow street, the deep sound never fails to seduce. The nice thing is that Volvo’s Johan Stenson, manager of the NVH (Noise, Vibration and Harshness) Centre at Volvo Cars, thinks exactly the same about it. He also enjoys the sound of Volvo's five-cylinder engines, and more especially the way they sounded in the very first Volvo 850. "That was a lovely, throaty gurgle - like rock & roll at its best!" he says. He now heads more than 60 people work to create the right sound pattern for Volvo's cars. The centre has recently opened a new acoustic laboratory, a reason to tell you more about this lab and the art of creating the “right” car sound.
Hans Knol ten Bensel
Close to reality…
The new acoustic laboratory is located in new premises in the very heart of the Volvo Cars production complex in Torslanda, Sweden. The chamber has a network of sound-absorbing protrusions , which are embedded in the walls and ceiling, to give optimal preconditions for testing engine noise. No background noise penetrates, no standing sound waves occur to disrupt the tests.
On the other hand, the acoustic lab's hard floor is a very realistic representation of the surfaces on which cars operate. It recreates the same sound effects as when driving on tarmac.
"With our new test chamber we can test four-wheel drive cars in an entirely different environment than we could previously," says Eva Lahti, acoustic engineer at Volvo Cars.
"Most of our work relates to creating the foundation for the best acoustic comfort from the customer's viewpoint. Customers who purchase a premium car expect that," says Johan Stenson, as we said the manager of the NVH Centre.
Volvo's are tested into the lab at power levels (and speeds) which are very close to reality...
Work on designing a car's sound is divided into three parts:
1. Sounds that irritate - for example squeaks and rattles, road rumble and wind roar.
2. Sounds that inform - for example engine noise and the "click" of various controls.
3. Sounds that impress - for example engine note and the sound of a door shutting.
It's all about eliminating sounds from the first category so that the others are heard as intended. Acoustic design has developed into something of a science among premium car manufacturers today. Having said that, it is a relatively new science.
The cars are put on a rolling bench to simulate actrual driving conditions...
"There's no long tradition in the sphere of acoustic design, but it is gaining in importance. Our challenge is to create an experience that delivers the right ‘Volvo sound'," says Johan Stenson.
The aim is to create typical "Scandinavian sound comfort" and an acoustic palette that matches the aura of the brand in terms of its core values of the environment, safety and design.
Scandinavian sound comfort
Eva Lahti explains what is meant by Scandinavian sound comfort:
"Here in Sweden and Scandinavia we have large, quiet spaces. The acoustic environment is open and free, not densely packed. And that's how our customers expect a Volvo to sound."
When it comes specifically to work on engine noise - the work that is done in the new noise lab - the focus is on two criteria: sound that informs and sound that impresses.
For engine noise that provides information, the experts aim for the optimal balance - the car's driving properties, road noise, steering feel and engine note should all create a single cohesive pattern.
"If I cruise at a steady speed, the engine should produce a pleasant, relaxing note. But if I accelerate from low speed under full throttle, the difference should be heard in the sound the engine produces. It should give me feedback to verify what I am doing so I do not lose my intuitive link with the car," explains Eva Lahti.
Johan Sensons just lives the deep troaty sound of the original 850 5 cilinder Volvo's. As an 850 owner, I just couldn't agree with him more...
Johan Stenson feels that the science of developing impressive engine sound can become an important competitive tool for securing customers
"For impressive engine sound, we have so far achieved the most striking results with our high-end products. The first car we worked on was the V8-powered Volvo XC90. We aimed to create a sophisticated V8 sound with a typical European note," says Johan Stenson.
How should plug-in hybrids sound?
In 2012, Volvo Cars will start marketing plug-in hybrids featuring a mixture of electric and/or diesel power. When the car is powered by electricity, progress is virtually silent. This means that other, more irritating, sounds will become more noticeable. This makes acoustic design very important. And things will be equally important from the traffic-safety viewpoint - it must be possible to hear an approaching car.
The control room of the new test lab.
Legal requirements will probably be implemented in most countries, and in fact some US states already apply such legislation. In Europe, there are discussions on just how quiet a car is allowed to be.
"So just how should our plug-in hybrid sound? So far we have no bank of experience from which to obtain data. We'll have to start examining this issue fairly soon," says Johan Stenson.
Some Facts of the new semi-acoustic test chamber…
The new facility has already entered full operation in the first half of 2009, and the building is insulated from vibration so as to avoid all outside interference. The test chamber in the three storey building is made of concrete and measures 22x15.9x6.75 metres. The measurement equipment is designed for use with both four-wheel drive and two-wheel drive cars, and maximum power output for the cars is an impressive 300 kW, so there is ample opportunity for high-performance testing, with speeds allowed to a maximum of 250 kph…
Hans Knol ten Bensel